Both partially or fully hydrolyzed polyvinylformamide (i.e., polyvinylamine) can be used as dry strength additives, wet strength additives, retention aids and drainage aids in papermaking. Polyvinylamine has a linear backbone structure and one primary amine group for every two carbon units, making it highly cationic in an aqueous system due to the high density of primary amine functionality. These polymers possess strong hydrogen bonding ability as a result of this high density of primary amine groups. U.S. Pat. No. 2,721,140 discloses use of polyvinylamine as an additive to make papers having high wet strength, while U.S. Pat. No. 5,961,782 discloses use of polyvinylamine to make crosslinkable creping adhesive formulations. U.S. Pat. No. 4,421,602 discloses a partially hydrolyzed, water-soluble polymer of N-vinylformamide that contains N-vinylformamide units and vinylamine units. It also discloses use of polyvinylamine and a 50% hydrolyzed polyvinylformamide to increase flocculation efficiencies, fines retention, and the drainage rate of pulp fiber in papermaking processes, while U.S. Pat. No. 6,159,340 discloses the use of such polymers as dry and wet strength additives in paper and paperboard production, U.S. Pat. Nos. 6,616,807 and 6,797,785 disclose use of polyvinylamines as drainage aids, flocculants, and retention aids in the paper making.
Polyvinylamines are typically made by solution, free-radical polymerization of N-vinylformamide monomer, followed by base- or acid-catalyzed hydrolysis, whereby the primary amine in the polymer backbone is deprotected, releasing formic acid. U.S. Pat. No. 4,774,285 discloses that N-vinylformamide monomer may be copolymerized with an additional vinyl monomer, e.g., vinyl acetate, and subsequently hydrolyzed to produce a water-soluble copolymer of vinylamine and vinyl alcohol, which may be used as wet and dry strength additives for papermaking. U.S. Pat. No. 5,630,907 discloses copolymer compositions containing both vinylamine and acrylic acid units, as well as their applications. U.S. Pat. No. 6,797,785 discloses copolymers containing vinylamine units in combination with either diallyldimethylammonium (chloride) (DADMAC) or acrylamide units via reverse emulsion polymerization, and their use as flocculants and coagulants in papermaking. EP 0251182 discloses copolymers containing vinylamine and acrylonitrile units for use in papermaking as drainage aids, retention aids, as well as wet end additives for increasing the dry strength of paper products. In general, these copolymers contain vinylamine units and additional vinyl units linked together randomly through carbon-carbon bonds in a linear fashion, where the additional vinyl units reduce the density of vinylamine units in the polymer backbone, thereby giving it a lower cationic charge density as compared to polyvinylamine homopolymer.
The amine functionality of polyvinylamine can react with a variety of compounds having reactive functional groups. Post-polymerization chemical modification of polyvinylamine with functional groups is an alternative approach to produce polyvinylamine derivatives with altered physical and application properties. U.S. Pat. No. 5,994,449 discloses a resin composition that is the reaction product of epihalohydrin with a mixture of a poly(vinylamine-co-vinyl alcohol) copolymer and a polyaminoamide, as well as the use of these compositions as a creping adhesives. U.S. Pat. No. 5,269,942 discloses the use of quaternized polyvinylamines for deinking loop clarification, and U.S. Pat. No. 5,292,441 discloses their use as flocculants for wastewater clarification. The quaternized polyvinylamines in these two instances are obtained from the reaction of polyvinylamine with a quaternizing agent, such as methyl chloride, dimethyl sulfate, or benzyl chloride. U.S. Patent Application No. US 2008/0009596 A1 discloses polyvinylamine-containing polymers that are modified by α,β-unsaturated alkyl carbonyl compounds, including amides, esters and acids. Particularly polyvinylamine-containing polymers modified with acrylamide showed particular effectiveness as additives in the papermaking process for improved dry strength paperboard products. U.S. Pat. No. 6,864,330 discloses a PEG grafted polyvinylamine derivative and also discloses that primary amines of the grafted polymer can be further cationized by reacting with an epoxide that contains the quaternary ammonium group. The grafted polymers are prepared by polymerizing vinylformamide in the presence of a PEG through free radical polymerization and are structurally different from polyvinylamine homopolymer and the copolymers. Vinylamine-containing polymers modified with butyl glycidyl ether are described in U.S. Pat. No. 5,324,787. Vinylamine-containing polymers modified with sodium chloroacetate are described in U.S. Pat. No. 6,133,392. U.S. Pat. No. 5,430,110 describes quaternized vinylamine-containing polymers, but does not describe their usefulness in enhancing the dry strength of a paper product or the enhancement of drainage of a papermaking system. Japanese Patent Application 10-110010A describes quaternized vinylamine-containing polymers, but does not articulate which specific compositions are most useful for dry strength of the paper product and drainage of the papermaking system. U.S. patent application Ser. No. 12/221,220 describes quaternized vinylamine-containing polymers. Compared to the present invention, U.S. patent application Ser. No. 12/221,220 presents a more specifically circumscribed portion of that invention wherein a polyvinylamine-containing polymer is preferably reacted with a quaternizing agent in a particular ratio that endows the resultant modified vinylamine-containing polymer with surprisingly high positive charge density, and exhibits unexpected enhanced dry strength, drainage, and fixative properties when used in papermaking applications.